Backing wheel for a belt grinder

ABSTRACT

A laminar backing wheel for the abrasive belt of a belt grinder or polisher has a disk of soft and resilient material compressed to one half or less of its relaxed axial thickness between two disks of stronger and more rigid material by threads stitched axially through the wheel. When the wheel stands still, or moves slowly, the tensioned belt rides over the circumferences of the more rigid material. At normal operating speed, the soft material of the first disk is caused to project beyond the more rigid disks by centrifugal forces and spreads axially into radial alignment with the more rigid disks to provide a soft backing for the belt while deformation of the wheel under starting stresses is resisted by the harder disks.

[ 1 June 17, 1975 1 BACKING WHEEL FOR A BELT GRINDER [75] Inventor: Herbert Stahl, Bottingen, Germany [73] Assignee: SM Maschinenfabrik Herbert Stahl,

Bottingen, Germany [22] Filed: Aug. 23, 1974 [2]] Appl. No.: 500,024

[30] Foreign Application Priority Data Aug. 24 1973 Germany 2342831 [52] US. Cl 51/135 R; 51/141; 74/2301 [51] Int. Cl B241) 21/00 [58] Field of Search 74/230.0l, 230.1, 230.7; 51/358,135 R, 141, 266, 170 B [56] References Cited UNITED STATES PATENTS 2,527.554 10/1950 Kimball 51/141 X 2,977,725 4/1961 Simendingcr 51/141 3.153.306 10/1964 Robischung 51/135 R 3,739,535 6/1973 Foumier 51/135 R Primary Examiner0the1l M. Simpson Attorney, Agent, or Firm-Hans Berman [57] ABSTRACT A laminar backing wheel for the abrasive belt of a belt grinder or polisher has a disk of soft and resilient material compressed to one half or less of its relaxed axial thickness between two disks of stronger and more rigid material by threads stitched axially through the wheel. When the wheel stands still, or moves slowly, the tensioned belt rides over the circumferences of the more rigid material. At normal operating speed, the soft material of the first disk is caused to project beyond the more rigid disks by centrifugal forces and spreads axially into radial alignment with the more rigid disks to provide a soft backing for the belt while deformation of the wheel under starting stresses is resisted by the harder disks.

10 Claims, 5 Drawing Figures BACKING WHEEL FOR A BELT GRINDER This invention relates to metal shaping apparatus, such as belt grinders and polishers, and particularly to a backing wheel for backing the abrasive belt of such metal shaping apparatus.

It is common practice to shape a workpiece by holding the workpiece in engagement with an abrasive belt backed by a wheel which drives the belt. To remove material, typically metal, from the workpiece uniformly and without starting marks, the backing wheel should be as soft and resilient as possible. However, the wheel must also transmit driving force to the belt, and the driving force, particularly the force transmitted to the belt during starting of the apparatus would permanently distort a very soft and resilient backing wheel, and the belt may be thrown off the wheel circumference if the latter does not maintain its circular cross section.

It was necessary heretofore to compromise between the two diametrically opposite requirements for a backing wheel of satisfactory consistency. The problem is encountered not only with wheels which are of uniform composition over their entire cross section, but also with wheels having a rigid core and a circumferential portion of more flexible material, such as rubber, plastic, or leather.

The primary object of the invention is the provision of a backing wheel for metal shaping apparatus of the type described which is soft and resilient enough during grinding or polishing to conform readily to the contour of a workpiece, yet is hard and rigid enough to with stand deformation under the driving stresses transmitted to the belt, particularly during starting from a standstill. Another object is the provision of a metal shaping apparatus employing the backing wheel of the invention.

With these and other objects in view, the invention provides a backing wheel of laminar structure. It includes first, second, and third, substantially circular disks, the first disk being coaxially fastened between the second and third disks under axial compression. Respective circumferential face portions of the second and third disks define a common surface of rotation, usually a cylinder, and the circumferential face portion of the first disk is substantially completely confined within the surface of rotation when the wheel does not rotate. The elastic modulus in tension of the material of the first disk is so much smaller than the corresponding moduli of the second and third disks to cause the circumferential face portion of the first disk to project radially beyond the afore-mentioned common surface under centrifugal forces when the wheel rotates at its normal operating speed. The axial compression of the first disk must be sufficient to cause the radially projecting face portion of the first disk to spread axially into radial alignment with the second and third disks.

Other features, additional objects, and many of the attendant advantages of this invention will readily be appreciated as the same becomes better understood by reference to the following detailed description of preferred embodiments when considered in connection with the appended drawing in which:

FIG. 1 is a fragmentary perspective view of a belt grinding machine equipped with a backing wheel of the invention;

FIG. 2a shows a first wheel of the invention in fragmentary section on its axis of rotation, the wheel being shown in its standing condition;

FIG. 2b shows the wheel of FIG. 2a in the condition assumed when rotating at its normal grinding speed;

FIG. 3a illustrates another wheel of the invention in the manner of FIG. 2a; and

FIG. 3b shows the wheel of FIG. 3a in its operating condition.

Referring initially to FIG. I, there is shown as much of an otherwise conventional belt grinding machine using a backing wheel of the invention as is necessary for an understanding of the invention.

The horizontal output shaft of an electric motor 2 carries a laminar wheel 4 whose several layers are fastened to each other by a spiral row of quilting stitches 43 terminating at a distance from the circumferential face of the wheel 4. A tensioning pulley 6 is mounted for rotation about an axis parallel to that of the wheel 8 in bearings, not shown, which are resiliently biased away from the wheel 6 so that a desired longitudinal tension is maintained in an abrasive belt 8 trained over the wheel 4 and the pulley 6 and traveling in the direction indicated by an arrow when the motor 2 is energized. A workpiece is normally ground on the illustrated apparatus by holding it against the belt-covered face portion of the wheel 4 indicated by the arrow 10.

The backing wheel illustrated in more detail in FIGS. 2a and 2b consists basically of three axially juxtaposed, practically circular disks. The axially central disk 41 consists of foam rubber or of foamed, elastomeric plastic, such as polyurethane. The two axially outer disks 42 consist each of multiple layers of cotton muslin. The three disks are fastened to each other by the textile threads of the stitches 43 which pass axially through the several layers and are so tight that the central elastomer disk 41 is axially compressed between the muslin disks 42. If permitted to relax, the elastomer disk 41 would expand to an axial thickness more than twice its illustrated thickness in the assembled wheel.

The outer circumferential faces of the three disks 41, 42 are located in a common, cylindrical surface of rotation about the wheel axis when the wheel 4 does not rotate. The belt 8, under these conditions, directly engages the face portions of the muslin disks 42, and these disks, of a material relatively hard and rigid, are not deformed when the motor 2 is started suddenly and while it accelerates to its normal working speed.

The centrifugal forces acting on the central elastomer disk 41, however, are sufficient to stretch the disk in a radially outward direction so that it projects beyond the circumferential faces of the muslin layers 42 which still define a surface of rotation, not significantly greater in diameter than the circummferential surface of the wheel at rest. Because the material of the elasto mer disc 41 was initially under severe compressive stress between the adjacent faces of the muslin disks 4], its projecting portion 44 spreads axially so that it is radially aligned with the two disks 42. Such spreading is enhanced by the radial pressure exerted by the belt 8.

At normal operating speed of the wheel 4, the belt 8 engages only the circumferential face portion 44 of the elastomer disk 41 and is radially separated by the soft, elastomeric material from the harder and more rigid, circumferential faces of the muslin disks 42.

The modified backing wheel shown in FIGS. 3a and 3b in the rest condition and at operating speed respectively differs from the first-described backing wheel by having two disks 41 of elastomeric foam material sandwiched between three muslin disks 42, the five layers of the wheel being fastened axially to each other by yarns 43 under sufficient tension to compress the foam disks 4] to about one third of their relaxed axial thickness, as evident from the lateral expansion of the projecting face portions 44 of the elastomeric disks at normal operating speed of the wheel.

The radial expansion of the elastomer disks 41 is limited mainly to those circumferential portions of the disks which extend radially beyond the outermost row of stitches 43. The portions of the disks 41 radially inward from the outermost row of stitches contribute little to the expansion, and no significant radially outward movement under centrifugal forces can be observed in those parts of the disks 41 separated from the free circumferential face by two or more rows of stitches. The softness of the backing provided by the wheel 4 to the traveling belt 8 at normal grinding or polishing speed can thus be selected by varying the radial spacing of the outermost stitches 43 from the wheel circumference.

While the elastomer disks 41 have been shown in FIGS. and 3a to be flush with the outer circumferential faces of the disks 42, this is not necessary for proper operation of the wheels of the invention. The softer and more resilient disks 41 contribute almost nothing to the deformation resistance of the wheel 4 during acceleration by the motor 2, and they may actually impair tracking of the belt 8 on the wheel surface during startup. It is desirable, therefore, that the outer face portion of the disk 41 be confined fairly completely within the surface of revolution defined by the muslin disks 42.

Muslin is widely used as a wheel or disk material in this field, but is not the only material which may be used to advantage as the harder or more rigid wheel material. Other materials are suitable if their elastic moduli in tension are much higher than the moduli of foam rubber or foam plastic which are the preferred elastomers for the wheels of the invention at this time. Outer fisks 42 made of fabrics other than muslin, and of fibers other than cotton have been used successfully, as well as metal disks, particularly aluminum disks employed either exclusively or combined with fabric layers in a single disk.

It should be understood, therefore, that the foregoing disclosure relates only to preferred embodiments of the invention, and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.

What is claimed is:

1. A rotatable, laminar backing wheel for an abrasive belt comprising:

a. a first substantially circular disk of a soft and resilient material having afirst elastic modulus in tension;

b. second and third substantially circular disks of materials having respective second and third elastic moduli in tension;

c. fastening means coaxially fastening said first disk between said second and third disks under axial compression,

I. said second and third disks having respective circumferential face portions defining a common surface of rotation, and said first disk having a circumferential face portion substantially completely confined within said surface when said wheel does not rotate,

2. said first modulus being sufficiently smaller than said second and third moduli to cause the circumferential face portion of said first disk to project radially beyond said common surface under centrifugal forces when said wheel rotates.

3. said compression being sufficient to cause the radially projecting face portion of said first disk to spread axially into radial alignment with said second and third disks.

2. A wheel as set forth in claim 1, wherein the axial thickness of said first layer under said compression is smaller than one half of said thickness of said first layer in the relaxed condition.

3. A wheel as set forth in claim 2, wherein the material of said first layer is foam rubber or foam plastic.

4. A wheel as set forth in claim 1, wherein said fastening means include at least one textile thread axially passing through said layers in a plurality of stitches, said face portion of said first layer being free of said stitches.

5. A wheel as set forth in claim 4, wherein said stitches extend in at least one arcuate row about the common axis of said disks.

6. A wheel as set forth in claim 5, wherein said row extends in a spiral about said common axis.

7. A wheel as set forth in claim 1, wherein at least one of said second and third disks essentially consists of textile material.

8. A wheel as set forth in claim 1, wherein at least one of said second and third layers includes metallic material.

9. A wheel as set forth in claim 8, wherein said metallic material is aluminum.

10. A metal shaping apparatus comprising:

a. a backing wheel as set forth in claim 1;

b. drive means for rotating said wheel about the common axis of said disks;

c. a pulley rotatable about an axis parallel to said common axis; and

d. an abrasive belt trained over the circumferences of said wheel and said pulley,

I. said belt engaging said circumferential face portion of said first disk and being separated thereby from the respective face portions of said second and third disks when said wheel rotates,

2. said belt engaging the circumferential face portions of said second and third disks when said wheel does not rotate. 

1. SAID SECOND AND THIRD DISKS HAVING RESPECTIVE CIRCUMFERENTIAL FACE PORTIONS DEFINING A COMMON SURFACE OF ROTATION, AND SAID FIRST DISK HAVING A CIRCUMFERENTIAL FACE PORTION SUBSTANTIALLY COMPLETELY CONFINED WITHIN SAID SURFACE WHEN SAID WHEEL DOES NOT ROTATE,
 1. A ROTATABLE, LAMINAR BACKING WHEEL FOR AN ABRASIVE BELT COMPRISING: A. A FIRST SUBSTANTIALLY CIRCULAR DISK OF A SOFT AND RESILIENT MATERIAL HAVING A FIST ELASTIC MODULUS IN TENSION; B. SECOND AND THIRD SUBSTANTIALLY CIRCULAR DISKS OF MATERIALS HAVING RESPECTIVE SECOND AND THIRD ELASTIC MODULI IN TENSION; C. FASTENING MEANS COAXIALLY FASTENING SAID FIRST DISK BETWEEN SAID SECOND AND THIRD DISKS UNDER AXIAL COMPRESSION,
 2. SAID FIRST MODULUS BEING SUFFICIENTLY SMALLER THAN SAID SECOND AND THIRD MODULI TO CAUSE THE CIRCUMFERENTIAL FACE PORTION OF SAID FIRST DISK TO PROJECT RADIALLY BEYOND SAID COMMON SURFACE UNDER CENTRIFUGAL FORCES WHEN SAID WHEEL ROTATES.
 2. A wheel as set forth in claim 1, wherein the axial thickness of said first layer under said compression is smaller than one half of said thickness of said first layer in the relaxed condition.
 2. said first modulus being sufficiently smaller than said second and third moduli to cause the circumferential face portion of said first disk to project radially beyond said common surface under centrifugal forces when said wheel rotates.
 2. said belt engaging the circumferential face portions of said second and third disks when said wheel does not rotate.
 3. SAID COMPRESSION BEING SUFFICIENT TO CAUSE THE RADIALLY PROJECTING FACE PORTION OF SAID FIRST DISK TO SPREAD AXIALLY INTO RADIAL ALIGNMENT WITH SAID SECOND AND THIRD DISKS.
 3. said compression being sUfficient to cause the radially projecting face portion of said first disk to spread axially into radial alignment with said second and third disks.
 3. A wheel as set forth in claim 2, wherein the material of said first layer is foam rubber or foam plastic.
 4. A wheel as set forth in claim 1, wherein said fastening means include at least one textile thread axially passing through said layers in a plurality of stitches, said face portion of said first layer being free of said stitches.
 5. A wheel as set forth in claim 4, wherein said stitches extend in at least one arcuate row about the common axis of said disks.
 6. A wheel as set forth in claim 5, wherein said row extends in a spiral about said common axis.
 7. A wheel as set forth in claim 1, wherein at least one of said second and third disks essentially consists of textile material.
 8. A wheel as set forth in claim 1, wherein at least one of said second and third layers includes metallic material.
 9. A wheel as set forth in claim 8, wherein said metallic material is aluminum.
 10. A metal shaping apparatus comprising: a. a backing wheel as set forth in claim 1; b. drive means for rotating said wheel about the common axis of said disks; c. a pulley rotatable about an axis parallel to said common axis; and d. an abrasive belt trained over the circumferences of said wheel and said pulley, 